Some do it in the comfort of home with a G&T to hand after a hard day at work. Others prefer it at the breakfast table over coffee; still more manage to tackle it on the train. But, wherever they are, those who know the pleasures it brings can be identified by the tell-tale combination of a furrowed brow, a well-sharpened pencil and a still sharper look in their eye.

The Daily Telegraph crossword - of which of course, I speak - has reached a milestone: tomorrow's will be the 25,000th. And yet, even as we celebrate its longevity, its future is by no means secure.

Sudoku, which many puzzle pundits thought would pass as quickly as a summer storm, has stubbornly endured, and with 5,472,730,538 possible combinations on a classic grid, it could be around for a while. But will the crossword?

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Our crossword editor, Val Gilbert, is uncertain: "The Telegraph crossword has been going for 81 years and I think it will last a century. Beyond that, I don't know. If you took a train journey 20 years ago, everybody was reading a paper, now people get their news from the television or online. Few have time to sit and think about the crossword."

Our leisure time is undoubtedly spent differently from that of early cruciverbalists. On the June day in 1925 when the first Daily Telegraph crossword was published, typical family entertainment might have included a game of whist or a radio play.

Telegraph compiler Don Manley says it was the perfect environment for crosswords to flourish. "I got my love of crosswords from my father; we didn't have a television and we'd sit together all evening solving them," he recalls. "My one sadness is that I haven't managed to pass that love on to my son. There are so many rivals for children's attention now."

And while television and the internet mean that younger people don't linger long over the back page, their lack of interest could also stem from a feeling that the clues, especially cryptic ones, require a depth of knowledge in the classics, literature and history that just isn't provided by the national curriculum.

"I think the only way we can secure a future for the crossword is to make sure we appeal to a younger audience, too," says Manley. "We need to start writing clues that they would be able to solve. Some are just too obscure."

This might also explain why sudoku - for which the only background knowledge you need are the numbers one to nine - has such mass appeal. Hazel Norris, Chambers's senior editor of crosswords games and puzzles, says: "There's been a lot of consternation in crossword circles about sudoku. Some fans think it will mean crosswords will die out, and there's no doubt that it's huge at the moment."

But she says that the new puzzle isn't the threat that crossword aficionados believe it to be. "What we're finding is that the sudoku craze is making people realise how gripping puzzles are and leading them to try crosswords for the first time. Sales of crossword dictionaries are as good as ever."

And there are other signs that the public is still hungry for the kind of brain teasers that characterise crosswords. Dan Brown puts his passion for planting clues down to a childhood spent working out anagrams and crossword puzzles. If as many of his fans develop a taste for them as relished his clues in The Da Vinci Code, then compilers had better get busy.

But Gilbert believes that crosswords have to evolve to survive. "To my mind, the internet isn't being used to its full potential with crosswords," she says. "You could have three-dimensional crosswords that would work on a cube - it would be a great new challenge for existing fans and might attract a new audience, too."

It's an idea that is beginning to take off; hundreds of online sites have emerged over the past few years, the Chambers Crossword Solver, which suggests solutions when you input the letters you know, is now available online and you can download crosswords for mobile phones and BlackBerrys.

There has even been an unexpected bit of celebrity endorsement for the old-fashioned paper variety: Hollywood "bad boy" Colin Farrell has apparently become hooked on the puzzles after a stint in rehab.

Norris can see why. "Once you've got the hang of the cryptic it is more addictive than sudoku," she says. "People will never complete a sudoku grid and say: 'that was a great 1,7,9 today', but they'll go on quoting their favourite crossword clues for ever."

•Don't miss the Telegraph's 25,000th crossword tomorrow and a chance to win a luxury weekend break

Three of the brains that leave you baffled

Don Manley

Don Manley was born in 1945 and grew up in rural Devon. He believes he inherited the crossword "gene'' from his father, who travelled between farms for work and would do a puzzle while drinking a pint en route.

When he was 17, he created a puzzle for a competition run by the London Evening News. He won and received a cheque for £2 2s. His first crossword was published in the Radio Times in 1964, while he was still a student.

Manley compiled crosswords for the Today newspaper after its launch in 1986. At his home in Oxfordshire, he was a neighbour of Colin Dexter and several other crossword enthusiasts, who all chivvied each other on.

In the mid-Eighties, his book, the Chambers Crossword manual, was published (a new edition is scheduled for October). "Thirty-four years passed from when I first wrote to the Telegraph to the day one of my puzzles was finally published,' he says. ''By knocking on the door for long enough I finally found my way in."

Roger Squires

Roger Squires lives in Shropshire and inherited his love of words from his poet grandmother and his father. Born in Tettenhall in 1932, he joined the Royal Navy at 15 and then spent 11 years in the Fleet Air Arm.

In 1961, he survived a ditching off Ceylon by escaping from his aircraft 60ft under the sea. Aircrew played cards for money but he was barred because he was a member of the Magic Circle, so he began solving crosswords. He started compiling his own and his first appeared in the Radio Times in 1963.

In 1978, Squires became the Guinness Book of Records' "World's Most Prolific Compiler", a title he still holds, with more than 65,000 published crosswords in over 470 publications.

Squires was crossword editor at the Birmingham Post for 22 years, and began compiling for The Daily Telegraph in 1986. He had stints on many other national and regional papers and his millionth clue appeared in The Telegraph in September 1989.

Ian Mawby

Ian Mawby was born in Newcastle in 1942 and now lives in Cambridgeshire. Aged 30, he became a professional racing driver and caught the eye of Lotus boss Colin Chapman. In 1973, Ian's brakes failed at 130 mph and he broke his neck in the crash. Although paralysed and confined to a wheelchair he still drives his 200 mph Mercedes.

In 2004, Ian sent a sample puzzle to The Daily Telegraph and his first puzzle was published in February 2005.

He wakes up almost every day with a clue ready-formed in his mind and jots down anything that strikes him as a good basis for others. He says his two careers have much in common. "I risked life and limb to thrill my fans when racing, but I was astonished when I discovered that the thrill of knowing one of my puzzles was going to be published was far superior to motor racing."

Crosswords down the years

1 In 1999, Anetta Duel, who had tackled the Telegraph crossword for 56 years, wrote her will on the crossword, just before she died, aged 99. The will was accepted.

2 The late cinematographer Adrian Biddle, who shot Aliens and the second Bridget Jones, was such a fan that he had the paper delivered on set every day, wherever he was.

3 In 1994, a reader wrote in to point out that, four days before the Estonian ferry disaster, the crossword had included the words Estonia, Disaster and Master Mariner.

5 Two days before the Dieppe raid in 1942, in which 4,500 Allied soldiers were lost, the word ''Dieppe'' appeared in the crossword.

6 In 1944, five top secret D-day code words appeared and MI5 investigated. Forty years later, it emerged that compiler Leonard Dawe, headmaster of the Strand School, had filled his grids with words suggested by his pupils, who socialised with American servicemen. None of them had known the significance of the words.

7 The Daily Telegraph's annual crossword competition is held in memory of the legendary compiler Bert Danher, who died in 2002. The trophies are presented by Sir Paul McCartney, who was Bert's nephew and godson.

9 During World War Two, The Daily Telegraph held its first crossword competition. Hopefuls had to complete it under exam conditions. The winner - F H W Hawes of Dagenham - finished in under eight minutes. MI5 invited the entrants to work as code-breakers at Bletchley Park.

10 When Saturday prize crosswords were introduced in 1928, the winners' lists included Stanley Baldwin, Sir Austen Chamberlain and Lord Russel of Killoween. The then Prince of Wales, who was "not very good at solving crosswords", never appeared, though his private secretary did.

'80 Years of Cryptic Crosswords' by Val Gilbert is available for £9.99 plus p&p from Telegraph Books on 0870 155 7222